I had a windscreen replaced last autumn after a stone cracked the screen directly in my eyeline.
My insurer, SAGA, use Nationwide Windscreens and I had to wait 4 weeks before they could source a replacement screen! It's a genuine Lexus screen that had to come from somewhere in Europe. The fitter, a mature chap who had been fitting screens for almost as many years as I've been driving, said Lexus always get OEM screens. He did a great job, was very respectful of my car. Everything worked as it should the ADAS systems were checked and at the time functioned as expected.
That all said my auto wipers are now behaving rather erratically and my dealership says there is no malfunctions but recommend the ADAS to be recalibrated. As the car is in for service next month I suggested they do this at the same time. Yes, no problem, that will be £400 and will take 3-4hrs!
It's something they cannot do themselves, it requires a huge amount of space to set up the various bits of kit, so they send the car to a local workshop that do nothing but ADAS calibrations. They also told me they do not replace screens themselves either, no dealership does, it's just not efficient or practical, they always get one of the local companies in. Unless the customer is paying they use whichever firm the customer's insurer uses.